In the following diagram, four different index fossils are labeled:

In this diagram, from top to bottom, an index fossil from the Jurassic period is labeled A, an index fossil from the Permian period is labeled B, an index fossil from the Devonian period is labeled C, and an index fossil from the Cambrian period is labeled D.

Public Domain

Which of the labeled fossils comes from the oldest organism?

A
B
C
D